This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-11-103618 filed on Apr. 1999, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a stator of an alternator for use in an automotive vehicle.
2. Description of Related Art
It is generally known to improve a space factor of a stator coil and thereby to decrease resistance of the coil and to increase an output of an alternator. It is important to increase the alternator output without increasing the alternator size, because electrical load in recent automobiles is becoming high. An example of an alternator in which the space factor is improved by inserting a coil having a rectangular cross-section into the stator slots is disclosed in JP-A-63-194543 (GB counterpart: GB-2,202,170A). Since the shape of the stator slot is substantially rectangular, the space factor becomes high when a coil having a rectangular cross-section is inserted therein, decreasing spaces formed between the slot and the coil.
It is also known to use plural conductor segments connected to one another to form a stator coil. For example, WO98/54823 (US counter part: U.S. Pat. No. 5,998,903) shows an stator in which U-shaped conductor segments having a rectangular cross-section are inserted into the stator slots from one end thereof, and open ends of the conductor segments are connected to one another at the other end of the stator slots. The stator coil is more easily formed by arranging the plural conductor segments than by winding a continuous wire.
However, in the stator disclosed in JP-A-63-194543, coil ends of the stator coil become bulky, and therefore the coil ends of each coil corresponding to respective phases accommodated in the same slot interfere with one another, because the rectangular cross-section of each coil changes to a round cross-section immediately after the coil comes out of the slot. The outer diameter of the coil ends become large, and accordingly a large frame for supporting the stator is required. This makes it difficult to reduce the size of the alternator. On the other hand, in the stator disclosed in WO98/54823, a conductor having the rectangular cross-section and a predetermined length has to be bent, or turned, at its middle portion to form the U-shaped conductor segment. When the rectangular conductor is bent, a large stress is imposed on the bending portion, thereby damaging an insulating film covering the conductor. This is detrimental to durability of the stator.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved stator of an alternator which has a high output in a compact size and high durability.
An alternator for use in an automotive vehicle is composed of a stator fixedly supported by a frame and a rotor rotatably supported in the stator. The stator includes a cylinder-shaped stator core having plural slots formed along the inner surface thereof and a stator coil disposed in the slots. The stator coil is formed by connecting plural U-shaped conductor segments, each segment having a pair of conductor portions, a turning portion connecting the pair of conductor portions and a pair of open end portions. The conductor portions are accommodated in the slots, the turning portions form a first coil end extending to one axial side of the stator core, and the end portions are connected to one another forming a second coil end extending to another axial side of the stator core.
Only the turning portion of each U-shaped conductor segment has a substantially round cross-section, such as a circular or oval cross-section, while all other portions have a flat rectangular cross-section. The U-shaped conductor segment may be made from a conductor bar having a uniform flat rectangular cross-section by deforming only the turning portion into a round cross-section. At least a part of the turning portion where a turning curvature is high is deformed into the round cross-section to prevent excessive stress from being imposed on the turning portion when the segment is bent into the U-shape.
Plural conductor portions may be inserted into each stator slot, and two kinds of U-shaped conductor segment, one being bent with a high curvature and the other with a low curvature, may be used. In this case, only the turning portion bent with a high curvature may be deformed into the round cross-section.
Alternatively, the stator coil is formed from a continuous conductor wire having plural conductor portions and turning portions connecting two neighboring conductor portions. In this case, too, only the cross-section of the turning portions is made round, while keeping other sections of the conductor wire including the conductor portions in the flat rectangular cross-section. The conductor portions are accommodated in the stator slots, and the turning portions extend to both axial sides of the stator core, forming coil ends at both sides.
According to the present invention, only the turning portions of the stator coil have a substantially round cross-section, while other portions including the conductor portion have a rectangular cross-section. Therefore, the stator coil is easily curved at the turning portions without damaging an insulator film covering the coil, and a space factor in the slot is increased. As a result, a compact alternator having a high output and a high durability is realized.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.